JP 10-211819A proposes a door control system that automatically closes vehicle doors. In this door control system, when an operation button provided in a portable device carried by a user is operated, a door closure command signal is transmitted from the portable device. On receiving the door closure command signal, the doors are closed.
In addition, another door control system is also proposed, which locks and unlocks respective vehicle doors, based on a result of ID code matching by mutual communication between a portable device (electronic key) and a vehicle unit. In this system, predetermined communication areas are set inside and outside a vehicle compartment, transmitters in the vehicle unit issue a request signal in each predetermined interval in the communication areas to perform code matching inside and outside the vehicle. In this way, approach to the vehicle, and getting on/off the vehicle by a user of the portable device are monitored.
By applying the door control system that uses mutual communication between a portable device and a vehicle unit to the vehicle door control system that automatically closes vehicle doors as proposed in JP 10-211819A, it is made possible to automatically close the vehicle doors, based on a result of ID code matching.
However, in the case of automatically closing doors, to prevent a portable device from being left confined within a vehicle compartment, it is necessary to detect its confinement. The confinement detection involves internal code matching when the user of the portable device has got off the vehicle, that is, when vehicle doors are open.
However, performing internal code matching with the vehicle doors open would expand a communication area originally set within a vehicle compartment to the outside of the vehicle compartment, because the vehicle doors are open. Expanding the communication area to the outside of the vehicle compartment might cause the possibility that the vehicle doors cannot be closed as a result of erroneous determination as if the portable device were within the vehicle compartment although it is actually outside the vehicle compartment. This will also arise when this door control system is applied to other objects such as a house.
To avoid such erroneous determination, it is possible to narrow the communication area. In this case, however, the confinement of the portable device may not be detected because of a narrowed communication area.